Split up PreferencesUI.py into individual files for each class, then fixed the imports everywhere that broke because of this.

flatcamGUI/preferences/OptionsGroupUI.py

@@ -0,0 +1,19 @@
+from PyQt5 import QtWidgets
+
+
+class OptionsGroupUI(QtWidgets.QGroupBox):
+    app = None
+
+    def __init__(self, title, parent=None):
+        # QtGui.QGroupBox.__init__(self, title, parent=parent)
+        super(OptionsGroupUI, self).__init__()
+        self.setStyleSheet("""
+        QGroupBox
+        {
+            font-size: 16px;
+            font-weight: bold;
+        }
+        """)
+
+        self.layout = QtWidgets.QVBoxLayout()
+        self.setLayout(self.layout)